Tens of thousands of students across the country walked out of their classrooms Wednesday and onto athletic fields and city streets as part of a massive ­national protest on gun violence spurred by a Florida high school shooting a month ago that left 17 dead.

The walkouts, which came 10 days before a march on Washington that could draw hundreds of thousands of students to the nation’s capital, are unprecedented in recent American history, not seen in size or scope since student protests of the Vietnam War in the late 1960s.

Supporters say the walkouts and demonstrations represent a realization of power and influence by young people raised on social media who have come of age in an era of never-ending wars, highly publicized mass shootings and virulent national politics.

The protests unfolded in ­major cities across the country — New York, Washington, Chicago, Seattle — and hundreds of smaller towns and communities as well.

In Maryland, students held pictures of the victims. At Columbine High in Colorado, the site 19 years ago of one of the first mass school shootings, students filed solemnly onto a soccer field and sent aloft balloons in memory of the victims there and in Florida. And at Marjory Stoneman Douglas High, where 14 students and three staff members were killed Feb. 14, students who were supposed to gather on the football field for 17 minutes and then go back to their classrooms, started walking — and kept walking to a park.

Students involved in the protests have been outspoken about their frustration with adults and political leaders who they believe have made them less safe by not doing more to curb gun violence or address school safety and mental health issues.

Many of the participants said the focus on gun control was not an expression of party preference. What they are demanding from Republicans and Democrats alike is action on an issue they believe has been put aside by lawmakers for too long. In an election year, with every seat in the House and a third of the Senate up for votes, the students are determined to make an ­impact.

“We want our Congress to know that some of us will be old enough to vote in the midterm elections, and the rest of us are going to be able to vote in 2020 or 2022, and they’re going to lose their job if they don’t do what we want to keep us safe,” said Fatima Younis, a student organizer with Women’s March Youth Empower, one of the lead coordinators of Wednesday’s walkouts. The group is demanding that lawmakers increase the age for people to purchase weapons, ban military-style weapons and demilitarize police ­forces.

Most of the student protests were approved by, and often coordinated with, school administrators. But there were reports of some schools where students were not allowed to hold protests or were penalized if they did.

In Washington, politicians and administration officials heard Wednesday’s message up close. Hundreds of high school and ­middle school students from local districts gathered at the White House carrying signs protesting gun violence and those who oppose gun-control measures. Just before 10 a.m., the crowd fell silent and sat down on Pennsylvania Avenue, their backs to the White House, with fists and signs held high. They sat quietly, one minute for each of the Stoneman Douglas victims. As the silence was broken at 10:17, the crowd began chanting, “We want change!”

In the District’s Capitol Hill neighborhood, students pushed through the doors at Stuart- ­Hobson Middle School, past the stone columns and into the streets, singing, “The power of one,” hoodies pulled up to ward off the cold. They held aloft homemade signs with slogans such as “My safety. Your safety,” as police motorcycles stopped traffic to let them cross busy streets.

“Hey hey, ho ho! Gun violence has got to go!” they chanted as they walked quickly to the Capitol grounds. People stepped out of nearby buildings and clapped and cheered as they walked past.

At the Capitol, many protesting students heard from lawmakers at an ­impromptu rally.

“I look at the crowd and I see the future, and I see you, and I came here to say thank you,” Rep. Luis Gutierrez (D-Ill.) said before leading the crowd in a “Si, se puede” chant, the Spanish phrase for “Yes, we can.” “Because I know you will accomplish what I and others have failed to do.”

At demonstrations across the country, in blue states and red states, the outpouring by students was an expression of grief and solidarity with schools and families that have experienced shooting deaths as well as a fierce warning to politicians to act.

At Columbine High, where shooters killed 12 students and one teacher in 1999, Myriah Murren, 14, told her mother “I love you” as she was dropped off before sunrise Wednesday. The freshman said she planned to walk out of class later in the morning to send a message to students who survived the shooting in Florida that she and her classmates “care for them.”

“A lot of people will join in,” she said, adding that going to a school that was the site of one of the earliest mass school shootings makes her and her classmates more aware of the issue.

At Minnetonka High School, southwest of Minneapolis-St. Paul, students walked out of classes on a cold late-winter morning saying they want politicians to take up their cause, even if they have to show them the way.

“We’re tired of sitting around and listening to politicians tell us what they are going to do without ever actually doing anything. And we’re also just kind of tired of adults not making it happen — adults saying what they are going to do and then just entirely blowing us off,” said Dominic Barry, 16, a sophomore at the school. “We’re the next generation for all these issues and we want people to know that we’re not going to sit around and let other people not take action on these issues.”

Students at Eastern High in Northeast Washington walked out of school into frigid temperatures. They poured onto the field carrying signs honoring the ­victims of Parkland, and surrounded their school’s track. While the school choir sang “Lean on Me” over the loudspeakers, students released 17 balloons for each of the 17 Parkland victims. Two students said each of their names aloud, then recognized the D.C. residents who lose their lives to gun violence each year.

Betty Luther, 16, said she knew something needed to change long before Parkland. The D.C. resident has lost family members and friends still in their teens to gun violence. But this is the first time she has protested, the first time she has locked arms with her classmates to show adults that they are demanding an end to the violence that has been so pervasive in her life.

“All I could think about is that it just has to stop,” said Luther, who was one of 17 students to hold an orange balloon during the ­walk-out.

The national walkouts faced a small number of counterprotests. Ethan Schmerer and Porter Kindall, students at Nampa High School in Nampa, Idaho, said the walkout promotes gun control, a stance they oppose. “We care about this issue because we want to defend our rights and let our voice be heard,” Schmerer told the Idaho Press-Tribune last week. While hundreds of Nampa students took part in Wednesday’s protest, about 50 joined the counterprotest, the the Idaho Press-Tribune reported.

At the University of Virginia in Charlottesville, still recovering from a violent white supremacist rally last summer, about 2,000 students gathered on the Lawn, many wiping away tears as the names of the 17 Florida victims were read aloud. The university’s chapel bells tolled 17 times as students bowed their heads in ­silence.

Parker Dymond, a freshman at St. Andrew’s Episcopal School in Potomac, Md., said after every school shooting, the students at the school observe a moment of silence.

It has become such a frequent occurrence, said Dymond, 15, that it no longer felt like enough.

So Dymond and a handful of other St. Andrew’s students skipped school Wednesday to protest in front of the White House and on the Capitol lawn and call for action on gun control.

“Our school had a ‘coming together’ instead of a walkout,” Dymond said. “But that felt disrespectful to me, to honor the victims but ignoring the reason they died.”

“Everything about this is political,” added Devin Lucas, 17, a junior at St. Andrew’s.

The response by students to the school shooting in Florida is different, Younis said, because “people thought we were too young to do anything, but students have just had enough. This shooting resonates with people because it could happen to any of us.”

At Walt Whitman High School in Bethesda, several hundred students walked out of class at 9:45 a.m. for a solemn 17-minute demonstration to honor the Florida shooting victims. They sat silently in the school bus drop-off zone on a bright, breezy morning as names of those shot and killed were read aloud one by one.

For each name on the roll call, one Whitman student stood up. These 17 designated students all wore orange T-shirts. Each held a sign with a victim’s name and picture, and each clutched an orange helium balloon. At the end of the ceremony, they released the balloons into the blue sky.

“Every time I looked at her face, I thought, ‘That could have been me,’ ” said Beverly Dempsey, 17, a Whitman senior. She stood for Gina Montalto, 14, who died at Stoneman Douglas a month ago.

President Trump and lawmakers are noting the role that students are playing in shaping the discussion on guns. The White House announced Sunday it is establishing a Federal Commission on School Safety to be headed by Education Secretary Betsy DeVos.

When Florida Gov. Rick Scott (R) signed a gun bill Friday that raises the minimum age to purchase a firearm to 21, he said, “To the students of Marjory Stoneman Douglas High School, you made your voices heard. You didn’t let up and you fought until there was change.”

Sen. Chris Van Hollen (D-Md.) told students on Capitol Hill he will help them vanquish opponents of changes to gun laws, including the National Rifle Association.

“We need to make sure that every member of Congress, Republicans and Democrats, people of all political stripes, are more afraid of the next school massacre, more afraid of the next death on our streets, more afraid of that, than they are of the NRA,” Van Hollen said. “Let’s go get them.”

Rep. Susan Davis (D-Calif.) posted on Twitter that she “walked out of Congress in solidarity with students in San Diego & across the nation calling for action to prevent gun violence.”

At Cactus Shadows High School in Cave Creek, Ariz., a 40-minute drive north of Phoenix, hundreds of students poured out of classrooms just before 10 a.m.

Gabe Ozaki, a 16-year-old junior, addressed his schoolmates first, saying, “Every person who has ever died in a school shooting started their day like we did today.” He went on to say that he thinks America is being robbed of its youth, but that he and others are energized by a wave of activism.

All but three of those who were killed at Stoneman Douglas were teenagers. For many of their peers, the list of their names and ages is a depressing reminder of the years stolen from them.

At George C. Marshall High School in Falls Church, several hundred students stood in the parking lot, their heads bowed in silence as the names of each of the victims in Parkland were read over a loudspeaker, one name per minute. Several students were in tears by the end, sharing hugs and vowing to keep fighting to keep schools safe from gun violence.

“It’s not so much the names, as the ages,” Ella Tynch, 16, said.

Maddie Salunga and two of her friends at the District’s Stuart-Hobson Middle School had been organizing for a month, selling homemade pins after school to raise money for Sandy Hook Promise, which aims to mobilize parents and schools to fight for stricter gun laws and to introduce gun violence prevention programs. They made signs and wrote speeches, too.

When they got close enough to see the dome of the Capitol, the whole group dashed toward it, as though playing tag, laughing.

But when the students stopped near the steps of the Capitol and passed around a megaphone, the group grew quiet, listening. Some students were angry that adults were unwilling or unable to prevent tragedies. They talked about dead bodies and students hiding under desks and parents whose children never came home.

Many said they were scared.

One girl burst into tears as she told the group she is afraid every single day at school. “That is not okay,” she sobbed, as other students nodded. “That is not okay.”

Samara Winston, 12, couldn’t understand why her generation is growing up with so much worry. “Kids just want to be happy. We just want to play.”

But here they were, talking about blood and guns.

A man stopped at the edge of the crowd to listen. He told them he had graduated from Stoneman Douglas.

He told them about driving to a funeral last month, and passing three others along the way.

“My generation did nothing,” Larry Vignola said.

“I’m really proud of your generation,” he said. He thanked them for speaking out.

At Hartford Magnet Trinity College Academy in Connecticut, high school students walked across the campus carrying poster-size pictures of the Parkland victims. Student organizers read each name and a brief biography before observing a moment of silence.

What started out as a remembrance turned decidedly political as students demanded Washington impose tougher gun laws to end school violence.

“We will not allow our elected officials to just tweet their thoughts and condolences without any gun reform,” said Larnee Satchell, 17, a senior at Hartford Magnet. “We need Congress to enact a resolution declaring gun violence a public health crisis. We need Congress to ban assault weapons and high-capacity magazines. We need Congress to expand background checks to all gun sales.”

Satchell was among several students at Hartford Magnet who worked with administrators to devise a plan for a peaceful demonstration. Principal Sally Biggs said district leaders encouraged schools to support students in their efforts to protest gun violence, but keep them on campus where they could remain safe. Several state and city leaders were on hand Wednesday to support the student demonstration.

“Our vision is for our students to be able to transform their world. This, today, is our vision in action,” Hartford Superintendent Leslie Torres-Rodriguez said Wednesday at Hartford Magnet. “We have to ensure that we create opportunities academically, socially and civically for our students to be critical thinkers, to look at a problem critically, assess the information and determine a solution.”

A week after the shooting, Alexa Marotta, 18, a junior and a student representative on the Hartford Board of Education, helped organize small group assemblies on safety protocols at Hartford Magnet. Those meetings evolved into planning sessions for the walkout, in which administrators encouraged students to create an event with purpose, Biggs said.

Students, she said, created lesson plans with topics on gun violence and school safety inspired by the Sandy Hook Promise, a planning guide for teachers that emerged after the 2012 shooting at the elementary school in Connecticut. Organizers said it was important to acknowledge Sandy Hook in recognition of the devastation gun violence has wrought in the state.

“It’s sad and terrifying that people think violence is the solution,” Marotta said. “It’s also tragic that those in need of help are often shunned by society before turning to violence. Everyone deserves better.”

At Nathan Hale High in Tulsa, about 200 students streamed out of school buildings and onto the football field, some holding signs and chanting, “Put the guns down!” The students universally said they want to feel safer at school, but had different ideas of how to achieve that.

The school has armed police officers patrolling the hallways, but after a spate of bomb threats this month, many students said they wanted to see metal detectors and bag checks. Earlier this month, students evacuated to the football field after a bomb threat. At the same time, there was a shooting at an apartment complex adjacent to the school. The sound of the shots that day sent the students running back inside the high school, where they went into lockdown mode.

Freshman MaKayla Woodard said what happened in Parkland weighed heavily on her and made her anxious to go to school.

“I’m walking out because they weren’t safe and we aren’t, either,” the 14-year-old said. The teen, whose father hunts, said she wants to see stricter background checks and mental health screenings for those seeking to buy guns. And she opposes President Trump’s proposal to arm teachers, saying she worries that a police officer will mistake an armed black teacher for an aggressor. “If a cop sees a black teacher with a gun, that teacher will get shot,” she said.

Adrian Gastelum, a 17-year-old junior, said he also wants to see stricter security. But as a gun owner, he does not believe stricter gun laws are necessary.

An earlier version of this story incorrectly identified Rep. Susan Davis of California as a Republican. She is a Democrat. The article also stated incorrectly that she joined House Republican leaders Wednesday at a news conference touting legislation that would provide additional security measures for schools. She did not.